1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2.!4)/.!,G0G0!.!,/5%G0G0#!22)%2G0G03934%-3%.%2!,G0G0#(!2!#4%2)34)#3G0G0#/-/.G0G04/G0G0!,!.!,/5%G0G0#!22)%2G1342!.3-)33)/.G0G03934%-3./)3%G0G0/“*%#4)6%3G0G01.2.2 the mean psophometric noise power over one mi
2、nute shall not exceed 50 000 pW0p for more than 0. 1 % ofany month;1.2.3 the unweighted noise power, measured or calculated with an integrating time of 5 ms shall not exceed1 000 000 pW0 (106pW0) for more than 0.01% (10-4) of any month.Note - For carrier transmission systems with one-minute mean noi
3、se power distributions which are not welldefined, the inclusion of another one-minute mean noise clause would be desirable to ensure equivalent performance forall systems. This clause would specify that:The mean psophometric noise power over one minute shall not exceed 20 000 pW0p for more than 3% o
4、f anymonth.This clause has not been specifically included because the CCIR has determined that for radio-relay links, theapplication of clauses 1.2.1 and 1.2.2 are sufficient to ensure, with high probability, that the additional clause will alsobe satisfied.1.3 If it is intended to use amplitude-mod
5、ulated voice-frequency telegraph equipment for 50 bauds conforming tothe Series R Recommendations and to obtain the quality shown in Recommendation F.10 1, the mean nonweightednoise power over 5 ms must not exceed 106pW0 during more than 0.001% (10-5) of any month, nor more than 0.1% ofany hour, for
6、 cable systems and for radio-relay links.If frequency-modulated voice-frequency telegraph equipment operating at 50 bauds is used, it is to be expectedthat the quality specified in 1.1 and 1.2 respectively above will be satisfactory as far as the telegraph transmission isconcerned.The conditions und
7、er which the above design objectives should apply are given in 2 below.2 Fascicle III.2 - Rec. G.2222 Conditions in which the design objectives for hypothetical reference circuits apply2.1 The values mentioned in 1 above are design objectives and it is not intended that they should be quoted inspeci
8、fications for equipment or used for acceptance tests. The noise on a homogeneous section of an actual carriersystem is dealt with in Recommendation G.226.The following Recommendations specify the conditions in which these general objectives apply to differenttypes of system, account being taken of t
9、he special characteristics of each system:- symmetric pair cable systems (Recommendation G.322);- symmetric pair cable “12 + 12“ systems (Recommendation G.326);- 4-MHz systems (Recommendation G.338 2), 12-MHz systems (Recommendations G.332 and G.339),18 MHz systems (Recommendation G.334) and 60 MHz
10、systems (Recommendation G.333) on 2.6/9.5-mm coaxial pairs;- systems on 1.2/4.4-mm coaxial pairs (Recommendations G.341, G.343, G.344, G.345 and G.346);- radio-relay links using frequency-division multiplex (Recommendation 393 3 of the CCIR).In particular, Recommendation G.442 lays down objectives f
11、or the use of amplitude-modulation voice-frequency telegraphy used in line-of-sight radio-relay systems.Tropospheric-scatter radio-relay systems should meet the objectives of this Recommendation, or otherobjectives, according to the circumstances of operation (see CCIR Recommendation 397 4).Other ob
12、jectives are recommended for systems providing 12 carrier circuits on an open-wire pair (seeRecommendation G.311).2.2 Designers are expected to fit their distribution curves to fall below both points given in 1.2.1 and 1.2.2above.2.3 In connection with 1.2.2 above, the CCITT would have preferred to
13、indicate a figure of 100 000 pW0p(average psophometric power over one minute at a zero relative level point), not to be exceeded during more than 0.01%of any month. On account of difficulties in measurement, a figure of 50 000 pW0p for 0.1% of any month has beenshown.2.4 Within each homogeneous sect
14、ion of a hypothetical reference circuit, the telephone channels will occupy thesame position in relation to each other. Within these sections, certain intermodulation products (those of odd order) tendto add on the basis of linear addition of voltages, but between sections it may be considered that
15、in respect of noise apower-additive law applies exclusively.In a part of a hypothetical reference circuit consisting of one or more equal homogeneous sections, the one-minute mean noise power not exceeded during 20% of any month shall be considered to be proportional to the numberof homogeneous sect
16、ions involved.2.5 In parts of a hypothetical reference circuit consisting of one or more equal homogeneous sections, the smallpercentage of any month in which the one-minute mean power may exceed the design objective for 0.1% of the time orless shall be regarded as proportional to the number of homo
17、geneous sections involved. This principle also applies to theobjective mentioned in 1.2.3 above.2.6 Although in principle it is to be understood that the general noise objectives are all-embracing, in practice it isrecognized that there will be abnormalities from time to time which will result in ad
18、ditional noise sources becomingevident. Often, such extra contributions can be accommodated within the margin available within the system design. Inother cases, no concern need be felt provided that such additional contributions are small compared to the generalobjective, for example, less than 10%
19、of the power or probability of occurrence respectively.In any case, all necessary precautions should be taken during the installation and putting into service of thesystems so that noises of external origin are reduced to a negligible value of, at the most, 10% of the limits fixed asobjectives.2.7 R
20、ecommendation G.223 gives the other hypotheses which are recommended for the calculation of the noise onthe hypothetical reference circuits for telephony.Fascicle III.2 - Rec. G.222 33 Circuits more than 2500 kilometres long3.1 The CCITT recognizes that in order to meet national and international no
21、ise performance objectives somelarge countries have found it necessary to introduce terrestrial FDM carrier transmission systems that are based on thehypothetical reference circuit described in Recommendation G.215. The noise performance objective for these systemscorresponds approximately to 5000 p
22、W0p on the 2500 km hypothetical reference circuit instead of the 10 000 pW0pmentioned in 1.2.1 and 1.2.2 above. These values include the noise contributed by multiplex equipment.3.2 The basic hypothetical reference circuit for satellite systems is defined in CCIR Recommendation 352, andprovisional n
23、oise objectives appropriate to the design of such systems in consideration of the values contained in 1above, are contained in CCIR Recommendation 353 6.4 Design objectives for noise produced by modulating equipments and additional equipmentsThe general objectives mentioned in 1 above include the no
24、ise produced by modulating and additionalequipments. The mean psophometric power, which corresponds to the noise produced by all modulating equipmentmentioned in the definition of the hypothetical reference circuit in question and by all additional equipment, should notexceed 2500 picowatts at a zer
25、o relative level point. This value of psophometric power refers to the whole of the noisedue to various sources (thermal noise, intermodulation, crosstalk, power supplies, etc.). Its allocation among the variousequipments can to a certain extent be left to the discretion of design engineers. However
26、, to ensure a measure ofagreement in the allocation chosen by different Administrations, the maximum values given in Table 1 /G.222 arerecommended for the modulating equipments.The allocation of a large part of the noise to channel-modulating equipment is justified because theseequipments are the mo
27、st numerous in a network and therefore are constructed as economically as possible.For the through-filters a noise objective of a maximum of 10 pW0p is recommended. This value refers to thenominal band of the through-connected groups; the noise outside that band must be considerably lower, to avoid
28、asignificant contribution of noise to channels situated in adjacent frequency bands.For other units of additional equipment (regulating equipment, equalizers, standby switching equipment, etc.) avalue of about 15 pW0p is indicated as a guideline to the designer.The above statement does not apply to
29、line standby switching equipment whose noise has to be consideredtogether with that of the line.The load assumption of through-filters and additional equipments should be in line with RecommendationG.223, G.228 and G.230. Account should be taken of the possible presence of additional signals outside
30、 the nominalfrequency band arising from adjacent channels.4 Fascicle III.2 - Rec. G.222TABLE 1/G.222a)No account is taken of the values attributed to pilot frequencies and carrier leaks.b)Valid also for 15-supergroup assembly modulators of the 60-MHz system (Recommendation G.333) to modulate from po
31、sitionNo. 3 into the line frequency position and vice versa.c)In the case of the 60-MHz system (Recommendation G.333) valid for the first modulating stage to bring the basic15-supergroup assembly into the frequency band of the basic supermastergroup and vice versa.Note - In Recommendation G.230 meth
32、ods for measuring the noise produced by modulating equipments are described.References1 CCITT Recommendation Character error rate objective for telegraph communication using 5-unit start-stopequipment, Vol. II, Rec. F.10.2 CCITT Recommendation 4-MHz valve-type systems on standardized 2.6/9.5-mm coax
33、ial cable pairs, OrangeBook, Vol. III-1, Rec. G.338, ITU, Geneva, 1977.3 CCIR Recommendation Allowable noise power in the hypothetical reference circuit for radio-relay systems fortelephony using frequency division multiplex, Vol. IX, Rec. 393, Dubrovnik, 1986.4 CCIR Recommendation Allowable noise p
34、ower in the hypothetical reference circuit for trans-horizon radio-relay systems for telephony using frequency division multiplex, Vol. IX, Rec. 397, Dubrovnik, 1986.5 CCIR Recommendation Hypothetical reference circuits for telephony and television in the fixed satelliteservice, Vol. IV, Rec. 352, D
35、ubrovnik, 1986.6 CCIR Recommendation Allowable noise power in the hypothetical reference circuit for frequency-divisionmultiplex telephony in the fixed satellite service, Vol. IV, Rec. 353, Dubrovnik, 1986.EquipmentMaximum valuecontributedby the sendand receive sidetogetherAssumptions about loadingC
36、hannel modulators 200 pW0pa)Adjacent channels loaded with: 15 dBm0 (Signal corresponding to Recommen-Other channels loaded with: 6.4 dBm0 dation G.227)Group modulators80 pW0pLoad in group to be measured: +3.3 dBm0Load in other groups: 3.1 dBm0 (each)Supergroup modulators 60 pW0p Load in supergroup t
37、o bemeasured: +6.1 dBm0Load in other supergroups: +2.3 dBm0 (each)Mastergroup modulators 60 pW0p Load in each mastergroup: +9.8 dBm0Supermastergroupb) modulators 60 pW0p Load in each supermastergroup: +14.5 dBm0Basic 15-supergroup assemblymodulatorsc)60 pW0p Load in each 15-supergroup:assembly: +14.5 dBm0
